Spain's Maverick Vinales, who won the season-opener in Qatar, continued his blistering form on Friday by setting the fastest time in practice for Sunday's Grand Prix of Argentina as his rivals struggled.
The 22-year-old clocked 1min 40.356sec on his Yamaha with Italian Ducati rider Danilo Petrucci and France's Johann Zarco, on another Yamaha, filling out the top three.
However, it was a miserable opening session for the sport's heavyweight stars with defending world champion Marc Marquez in 11th on a Honda, Ducati's Jorge Lorenzo down in 15th and nine-time world champion Valentino Rossi, the teammate of Vinales, almost a second off the pace in 16th.
1. Maverick Vinales (ESP/Yamaha) 1:40.356, 2. Danilo Petrucci (ITA/Ducati) at 0.206, 3. Johann Zarco (FRA/Yamaha Tech 3) 0.218, 4. Jonas Folger (GER/Yamaha) 0.304, 5. Karel Abraham (CZE/Ducati) 0.322, 6. Andrea Iannone (ITA/Suzuki) 0.345, 7. Andrea Dovizioso (ITA/Ducati) 0.360, 8. Hector Barbera (ESP/Ducati Avintia) 0.497, 9. Jack Miller (AUS/Honda Marc VDS) 0.511, 10. Alvaro Bautista (ESP) 0.580
11. Marc Marquez (ESP/Honda) at 0.602, 15. Jorge Lorenzo (ESP/Ducati) 0.772, 16. Valentino Rossi (ITA/Yamaha)
1. Lorenzo Baldassari (ITA/Kalex) 1:44.943, 2. Franco Morbidelli (ITA/Kalex) at 0.224, 3. Thomas L�thi (SUI/Kalex) 0.373
1. Joan Mir (ESP/Honda) 1:51.559, 2. Gabriel Rodrigo (ARG/KTM) at 0.209, 3. Nicolo Bulega (ITA/KTM) 0.359